1. Field of the Invention
The present invention relates to a position detecting apparatus and to a semiconductor device producing method using the position detecting apparatus, which are suitable for use when, for example, relative in-plane alignment between a first object and a second object is conducted in an exposure device for producing semiconductor devices to expose and transfer a minute electronic circuit pattern formed on the surface of the first object, such as a mask or a reticle (hereinafter, referred to as a "mask") onto the surface of the second object, such as a wafer.
2. Description of the Related Art
In conventional exposure apparatus for producing semiconductor devices, relative alignment between the mask and the wafer has been an important factor to improve performance. In particular, in recent exposure apparatus, there is a demand for relative alignment of high accuracy, which is on the order, for example, of submicron or less to provide more highly integrated semiconductor devices.
The distance between the mask and the wafer is measured by an inter-plane distance measuring device or the like. After the distance has been measured and control has been effected so as to attain a predetermined distance value, alignment between the mask and the wafer is effected by utilizing positional information obtained from so-called alignment patterns provided on the mask and the wafer surfaces. Various methods are available for this alignment. For example, the amount of deviation between the alignment patterns is detected by performing image processing. Alternatively, as proposed in U.S. Pat. No. 4,037,969 and Japanese Unexamined Patent Publication No. 56-157033, a zone plate is used for an alignment pattern; a beam is applied to this zone plate, and the position of a convergent point in a predetermined plane of a beam outgoing from this zone plate is detected.
Generally speaking, when compared with methods that simply use an alignment mark, the method using a zone plate is more advantageous in that an alignment of relatively high accuracy is possible without being affected by any defect in the alignment mark.
FIG. 12 is a schematic diagram showing a conventional position detecting device using zone plates.
In FIG. 12, a parallel beam emitted from a light source 72 is transmitted through a half mirror 74, and then condensed at a converging point 78 by a condensing lens 76. After this, the beam is applied to a mask alignment pattern 168a on a mask 168 and a wafer alignment pattern 160a on a wafer 160, placed on a support base 162. These alignment patterns 168a and 160a are formed by reflection-type zone plates, each forming a converging point in a plane orthogonal to the optical axis that includes the converging point 78. Any deviation in the converging point 78 in the orthogonal plane at this time is transmitted to a detector 82 by the condensing lens 76, half mirror 74 and a lens 80 and is thereby detected.
Then, in accordance with an output signal from the detector 82, a driving circuit 164 is driven by a control circuit 84 to effect relative alignment between the mask 168 and the wafer 160.
FIG. 13 is a diagram illustrating the image formation relationship between the beams from the mask alignment pattern 168a and the wafer alignment pattern 160a shown in FIG. 12.
In FIG. 13, part of the beam diverging from the converging point 78 is diffracted by the mask alignment pattern 168a to form, in the vicinity of the converging point 78, a converging point 78a indicating the mask position. The remaining part of the beam is transmitted through the mask 168 as zero-order transmitted light and impinges upon the wafer alignment pattern 160a on the wafer 160 without change in the wavefront. At this time, the beam is diffracted by the wafer alignment pattern 160a, and then transmitted through the mask 168 again as zero-order transmitted light before it is condensed in the vicinity of the converging point 78 to form a converging point 78b indicating the wafer position. In FIG. 13, when the beam diffracted by the wafer 160 forms a converging point, the mask 168 is simply transmissible.
The position of the converging point 78b due to the wafer alignment pattern 160a thus formed is formed as a deviation amount .DELTA..sigma.' corresponding to a deviation amount .DELTA..sigma. along the plane that is orthogonal to the optical axis that includes the converging point 78, in accordance with the deviation amount .DELTA..sigma. of the wafer 160 with respect to the mask 168 in the direction along the surfaces of the mask/wafer (lateral direction).
It is generally known that when a pattern on a mask is exposed on a wafer to produce a semiconductor device, the mask pattern formed on the wafer is shifted due to exposure distortion. In view of this, when performing relative alignment between the mask and the wafer, various measures are taken, taking this shift amount into consideration, beforehand.
In the position detecting method using a conventional exposure device for producing semiconductor devices, in which relative alignment between first and second objects is conducted using an alignment mark previously exposed on the second object (wafer) and an alignment mark on the first object (mask), exposure distortion is generated due to the limits of the exposure light source, so that exposure is sometimes effected with the exposure position of the alignment mark exposed on the second object being shifted from a step exposure position. Thus, the alignment mark on the first object is aligned with respect to the alignment mark, which has shifted from the predetermined exposure position, on the second object, with the result that the relative alignment cannot be conducted correctly.
Further, even when the exposure distortion is taken into account and each point in the shot is arranged on the first object, with the corresponding shift amount being set in each pattern (including the alignment mark), alignment cannot be conducted correctly when relative alignment is effected by using the alignment mark on the first object and the alignment mark on the second object, which is affected by exposure distortion.